import math

def distance(a, b):
    dx = abs(a[0]-b[0])
    dy = abs(a[1]-b[1])
    return math.sqrt(dx*dx + dy*dy)

if __name__ == '__main__':
    x1, y1, x2, y2 = map(float, input().split())
    print(distance((x1, y1), (x2, y2)))
 import math math def distance(a, b):
    dx = abs(a[0]-b[0])
    dy = abs(a[1]-b[1])
    return math.sqrt(dx*dx + dy*dy) distance dx = abs(a[0]-b[0]) dx abs(a[0]-b[0]) abs a[0]-b[0] a[0] a 0 b[0] b 0 dy = abs(a[1]-b[1]) dy abs(a[1]-b[1]) abs a[1]-b[1] a[1] a 1 b[1] b 1 return math.sqrt(dx*dx + dy*dy) math.sqrt(dx*dx + dy*dy) math.sqrt math sqrt dx*dx + dy*dy dx*dx dx dx dy*dy dy dy a a b b if __name__ == '__main__':
    x1, y1, x2, y2 = map(float, input().split())
    print(distance((x1, y1), (x2, y2))) __name__ == '__main__' __name__ '__main__' x1, y1, x2, y2 = map(float, input().split()) x1 map(float, input().split()) map float input().split() ().split () input split y1 x2 y2 print(distance((x1, y1), (x2, y2))) print distance((x1, y1), (x2, y2)) distance (x1, y1) x1 y1 (x2, y2) x2 y2 x2, y2 = map(float, input().split()) map(float, input().split()) x2 y1, x2, y2 = map(float, input().split()) map(float, input().split()) y1 y2 = map(float, input().split()) map(float, input().split()) y2 x1, y1, x2, y2 = map(float, input().split()) map(float, input().split()) x1 def distance(a, b):
    dx = abs(a[0]-b[0])
    dy = abs(a[1]-b[1])
    return math.sqrt(dx*dx + dy*dy) def distance(a, b):
    dx = abs(a[0]-b[0])
    dy = abs(a[1]-b[1])
    return math.sqrt(dx*dx + dy*dy) distance
import math

def distance(a, b):
    dx = abs(a[0]-b[0])
    dy = abs(a[1]-b[1])
    return math.sqrt(dx*dx + dy*dy)

if __name__ == '__main__':
    x1, y1, x2, y2 = map(float, input().split())
    print(distance((x1, y1), (x2, y2)))

